(1) Field of the Invention
The present invention generally relates to a folding device. More particularly, the present invention relates to second-fold rollers for a folding device adapted for cutting and folding superposed paper webs into a folded section of superposed sheets.
(2) Description of the Prior Art
A conventional folding device for a web rotary press performs its folding operation in the following manner:
A paper web is subjected to a vertical folding motion between a former and a nipping roller unit arranged below the former. This vertically folded paper web is wrapped around a folding cylinder by holding the forward end of the web by means of pins fixed on the folding cylinder. The folded web is cut into a sheet of predetermined length by a cutting knife fixed in a cutting cylinder which is arranged in parallel to the folding cylinder. Further, the substantially center of the cut sheet is forcibly inserted into the narrow space between a pair of second-fold rollers by a folding knife fixed on the folding cylinder. This narrow space is so controlled as to be equivalent to the thickness of the cut sheet to be folded.
Finally the cut sheet is laterally folded by restraining between the second-fold rollers.
Such a conventional folding manner is broadly well known by several printed matters such as "Shinbun Insatu Insatu-Hen Kaitei-Ban (Newspaper Press, Printing Edition Revised Version)" edited by Nippon Shinbun Kyokai Kohmu-Linkai (Japan Newspaper Institute, Engineering Commission), Oct., 31, 1975 pages 47 to 48.
According to this publication, the conventional web folding device has employed a specially designed second-fold roller to conduct the nipping operation. In detail, such a fold roller has been provided with stripes or diamondwise pattern formed in its cylindrical surface. Further, another prior art (Japanese utility model Publication No. Sho.59-29008) shows a second-fold roller formed with groove(s) in addition to the stripes or diamondsise pattern and a pair of drag rollers formed with circumferential grooves of predetermined depth and width. These circumferential grooves for the drag rollers are formed in its respective ends so as to contact with each corner of the cut sheet for another purpose.
However, in such conventional folding devices, the rear end of the paper web is cut by the cutting knife and the front end of it is released from the pin of the folding cylinder when the second-fold rollers hold the paper section to be laterally folded. On this occasion, the four corners of the paper sheet are isolated from the cylindrical surface of the folding cylinder. Even if a paper guide is set along the folding cylinder, the cut sheet can be freely moved between the paper guide and the folding cylinder. The cut sheet is accidentally and irregularly folded and the irregularly folded sheet is applied with nipping force by the second-fold rollers. This will often generate undesirable folded sections such as dog ears.
Further, the paper web is always applied with nipping force from the moment when the section to be laterally folded is nipped to the moment when the paper web is wholly fed out of the folding device. For example, folding works for a lot of pages, such as a newspaper, may often have trouble such as waving when the narrow space between the second-fold rollers is not correctly arranged and/or vertically folded sections of the webs become thicker than the other end. This waving phenomenon causes folded wrinkles when this waving becomes so hard that paper webs can not be smoothly moved.
In order to overcome these problems, the inventor of the present application has provided a specially designed second-fold roller pair to improve its lateral folding and web/sheet feeding functions in the previously applied invention; Japanese Utility Model, Application No. Sho.60-47057, Japanese UM Provisional Publication No. 61-176150. Although this specially designed second-fold roller is remarkably effective to a thick paper folding work, it can not adapt to a thin paper folding work. In detail, both edges of such thin paper tend to flutter and this flutter causes dog-ears at the corners of the paper sheet. Further, this specially designed second-fold roller pair can not completely nip the vertically folded section fed from the former.